The creator of "The Simpsons" says Smithers was color incorrect when he first appeared on the show ... black.
Waylon Smithers' black hue was simply a mistake, but producers didn't have the money to turn him to his intended yellow ... so says Matt Groening.
Groening gives an interesting explanation for the error, which was short-lived. It was corrected for Smithers' second appearance in the town of Springfield ... whatever state it's in.
Groening also tells us why all the other characters are yellow ... and it's not what you'd expect.